The patch implements the following logic:
- always warn if disk have GPT
- in interactive mode: explicitly warn that any change to MBR will
result in GPT removal, ask for confirmation, and remove GPT
- in non-interactive mode: remove GPT and explicitly note this fact

Wouldn't it be more reasonable to have a new command-line option to
remove the GPT? In non-interactive mode without the new option, if the
GPT exists the command should fail with a non-zero exit status (and an
appropriate error message).